1. Field of the Invention
The present invention relates to a liquid-crystal display unit for a camera, and more particularly, to a liquid-crystal display unit for a camera which has a reflective liquid-crystal panel.
2. Description of the Related Art
In recent years, for example, a liquid-crystal display unit having a liquid-crystal panel or the like has generally been used in practice as a display unit for displaying various information for a camera or the like designed for photography or the like.
A liquid crystal applicable to the liquid-crystal panel or the like does not glow by itself. For example, under a low-luminance environment such as at night or in a dark room, it becomes difficult to discern various information appearing on the liquid-crystal panel of the liquid-crystal display unit. In an effort to readily discern various information appearing on the liquid-crystal panel under a low-luminance environment, various proposals have been made for a liquid-crystal display unit in which a light-emitting device such as a light-emitting diode (hereinafter LED) is placed on the back side of a liquid-crystal panel or the like in order to illuminate the liquid-crystal panel or the like from the back side thereof. Such liquid-crystal display units have been put to practical use.
For example, a liquid-crystal display unit (LCD illuminating device for a camera) disclosed in Japanese Patent Laid-Open No. 2-53040 is such that a translucent liquid-crystal panel of a liquid-crystal display (hereinafter LCD) placed in a housing of a camera is illuminated from the back side thereof using a lighting device. The brightness of the back side of the liquid-crystal panel is measured. If a measured value is lower than a given value, the illuminating device is lit.
The structure of the LCD unit having a liquid-crystal panel will be described briefly. As shown in FIG. 10, a translucent reflection plate 102 is placed behind a translucent liquid-crystal panel 101. An auxiliary light illuminating device 104, and a photometry means (not shown) for measuring the brightness on the back side of the liquid-crystal panel 101 are placed behind the translucent reflection plate 102.
External light 103 such as daylight or bright room light is measured by the photometry means. If the measured value sufficiently exceeds the given value, light originating from the external light 103 is transmitted by the liquid-crystal panel 101, and then reflected by the translucent reflection plate 102. The reflected light is irradiated from the back side of the liquid-crystal panel 101. Thus, the display of various information appearing on the liquid-crystal panel 101 can be discerned readily.
If the measured value of the external light 103 provided by the photometry means is lower than the given value, the auxiliary light illuminating device 104 placed behind the translucent reflection plate 102 is lit. The illumination light emanating from the auxiliary light illuminating device 104 is transmitted by the translucent reflection plate 102, and then irradiated from the back side of the liquid-crystal panel 101. Thus, the display of various information appearing on the liquid-crystal panel 101 can be readily discerned.
The liquid-crystal panel having the aforesaid structure shall be referred to as a reflective liquid-crystal panel.
The structure of the LCD unit having the reflective liquid-crystal panel will be described in more detail. As shown in FIG. 11, the reflective liquid-crystal panel 101 comprises two glass plates arranged above and below with a liquid crystal locked in between them; that is, an upper glass plate 111 and lower glass plate 114, an upper polarization plate 115 affixed to the top of one of the two glass plates 111 and 114, a lower polarization plate 119 affixed to the bottom of the other glass plate, and a translucent reflection plate 102 arranged under the lower polarization plate 119.
The two glass plates of the upper glass plate 111 and lower glass plate 114 are opposed to each other. Segment electrodes 112 and common electrodes 113 are placed on the inner sides of the glass plates. A light distribution membrane 116 is placed on the inner sides of the segment electrodes and common electrodes. The segment electrodes 112 and common electrodes 113 are thus coated with the light distribution membranes 116 respectively. A liquid crystal 118 is locked in the innermost space.
A sealant 117 is interposed between the two glass plates; the upper glass plate 111 and lower glass plate 114. With the sealant 117, the lateral side of the liquid crystal 118 is sealed up.
The upper polarization plate 115 is placed on the top side of the upper glass plate 111. The lower polarization plate 119 is affixed to the bottom side of the lower glass plate 114.
In the reflective liquid-crystal panel 101 having the foregoing structure, the translucent reflection plate 102 and the LED 104 for backlighting that is an auxiliary light illuminating device are placed under the lower polarization plate 119. An LED drive circuit 104a is electrically connected to the backlighting LED 104.
In the liquid-crystal panel 101 of the LCD unit, for displaying given characters or graphic information, an LCD drive circuit (not shown) is used to apply a voltage between the segment electrodes 112 and common electrodes 113 so that the alignment of molecules of the liquid crystal 118 can be made different from the alignment occurring in an initial light distribution state. Transmission of incident light is thus controlled, whereby characters, graphic information, or the like can be contrasted to be discernible.
As mentioned above, in the LCD unit, the translucent reflection plate 102, placed on the back side of the liquid-crystal panel 101, backlighting LED 104 serving as an auxiliary light illuminating device, and LED drive circuit 104a for driving the LED are arranged as an illuminating means for illuminating the liquid-crystal panel 101 from the back side thereof.
When a camera or the like in which the LCD unit having the reflective liquid-crystal panel 101 is employed is used to perform photography or the like, if the discernible degree of various information on the liquid-crystal panel 101 deteriorates because photography is performed in a low-luminance environment such as at night or in a dark room, the LED drive circuit 104 is actuated in order to light the backlighting LED 104. Light emanating from the backlighting LED 104, as described in conjunction with FIG. 10, is transmitted by the translucent reflection plate 102 and illuminates the liquid-crystal panel 101 from the back side thereof.
For example, a light accumulator of a self-glowing type such as a luminous paint has generally been known in the past. When daylight or the like is irradiated to this type of light accumulator, light accumulation is effected (light is accumulated). The light accumulator then glows by itself in the low-luminance environment or the like.
The mechanism of the self-glowing is such that: when a light accumulator having a rare earth element or the like as a glowing source receives, for example, radiation or infrared rays, electrons are temporarily excited to enter a highly-energized state; and when the excited electrons return to the original state, light is emitted.
In recent years, various proposals have been made for an LCD unit in which an additive or the like is mixed in a light accumulator, measures are taken so that it will take much time for excited electrons to return to the original state, and thus the glowing time of the light accumulator is made longer.
However, according to a means disclosed in the Japanese Patent Laid-Open No. 2-53040, a power supply is needed for lighting the auxiliary light illuminating device 104. When the LCD unit concerned is employed in a camera or the like, it becomes necessary to take measures including a measure of supplying power required for lighting the auxiliary light illuminating device 104 from a camera body. The power consumption in the camera body therefore increases. A large battery must therefore be employed in a camera body. This poses problems that a camera becomes large in size and that a power saving is crippled.
Furthermore, there is a problem that since various relevant members including a drive circuit for driving a light-emitting device such as an LED, a judging means for judging whether or not to execute illumination, and a switching means needed for illumination become necessary, an LCD unit itself or a camera in which the LCD unit is employed becomes large in size and results in high costs.